Or it can be a blip in the software on Afterburner. Or in Firestrike. Or the hardware reporting. Or any number of things.

nothing to worry about

Some benchmark runs have periods of loading, transitions, or even just odd spots that consistently spike up/down no matter what. Even if it is consistent in this one benchmark, I'd argue its likely nothing to worry about if it happens in the same spot and doesn't affect the overall score compared to similar units.